Economically priced electronic calculators are becoming a means to be used by educators for teaching mathematics at all grade levels. It has been suggested that the electronic calculator, particularly when used with specially prepared teaching materials, such as the Elementary Mathematics Concepts with Calculators Program published by Texas Instruments Incorporated, is a valuable tool for teaching elementary arithmetic and logical reasoning to children in the first through sixth grades. However, when introducing the basic concept of our number system to a young child, it has been suggested that a special electronic calculator be provided to the child. Such a calculator preferably performs the most simple functions. For example, such a calculator may have merely zero and one numeral keys and plus, equal and clear function keys. Then as the pupil exhibits an understanding of the meaning of the aforementioned numerals and functions and acquires skills in understanding basic mathematical concepts, it has been suggested that the child be provided with increasingly more sophisticated calculators. The calculator used at the end of this learning cycle might be equipped to perform the four basic arithmetic functions using all ten digits of our decimal number system, for instance.
It has been suggested that the ability to provide school children with such a varied range of electronic calculators, would be a valuable teaching tool to augment the more traditional teaching tools presently used to teach elementary grade children simple arithmetic concepts and principles. It has been further suggested, that in lieu of manufacturing individual calculators having the aforementioned range of capabilities, that a full four function electronic calculator be provided with a plastic mask. The mask would overlay the calculator and be provided with openings which would align with selected key push buttons on the calculator. These openings would permit the child to access only selected keys when the mask was in place. It has been found, however, that providing such a full function calculator with a plastic mask permitting access only to selected keys has certain disadvantages. The disadvantages include the propensity of the mask to be easily removed from the calculator and inadvertent operation of covered key push buttons by the child. This latter problem arises due to the fact that the mask typically must be made from very thin plastic to permit access to desired keys; but the thinness of the plastic often fails to prevent inadvertent operation of the covered keys when the pupil merely lies his hand across a portion of the calculator keyboard covered by the mask.
It is therefore one object of this invention to provide an electronic calculator capable of being configured to permit entry of only selected numerals and selected functions. It is a further object of this invention to permit the configuration of the selected numerals and selected functions enterable to be altered at a school or other point of use without requiring major disassembly of the calculator. It was another object to prevent inadvertent operation of keys not included in the configuration selected.
It is still yet another object of this invention to provide a calculator with an interchangeable keyboard, the calculator typically being provided with a plurality of such interchangeable keyboards and the plurality of interchangeable keyboards being provided with different preselected configurations of numeric and/or function keys.
The foregoing objects are achieved according to the present invention as is now described. In a preferred embodiment of the invention, an electronic calculator preferably having an integrated circuit, a display for displaying a number outputted by the integrated circuit, an array of key switches for inputting numeric and functional data into the integrated circuit and a case in which the integrated circuit, display and array of key switches are disposed is preferably provided with a removable keyset. The removable keyset preferably includes an array of key switches push buttons moveably disposed in openings in a member retaining the array of key switch push buttons and the case is preferably provided with an opening for receiving the removeable keyset. When removeably received in the opening, the array of key switch push buttons is operationally disposed adjacent to the array of key switches, thereby permitting the input of numeric and functional data when particular key switch push buttons are depressed causing actuation of the adjacently disposed key switches. The case is also preferably provided with a release plunger and locking mechanism permitting the key set to be temporarily locked into place in the opening in the case. Preferably, the electronic calculator is provided with a plurality of such keysets, the keysets being provided with different configurations of key switch push buttons. The plurality of removeable keysets may be interchanged to present an operation with a selected configuration of key push buttons, whereby the operator can input only selected numeric functional data according to the key switch push buttons provided in the keyset then positioned in the opening in the calculator's case.